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The lowest flower in the pear (Pyrus communis L.) cluster usually develops and blooms first and also has a greater sink potential. For this reason, resources are preferentially utilized by the lowest fruit, and this is also one of the reasons why most thinning practices tend to favor their set. However, it is not always possible to perform selective thinning. This study was undertaken to determine if hindering pollination in the most developed flowers in the cluster influences yield or quality compared to that obtained in a whole open-pollinated cluster. The treatments were made in `Blanquilla' (Spadona, Agua de Aranjuez) and `Conference' pear within a wide range of flower densities for each cultivar. Pollination was hindered by cutting off the flower styles. The factor tested was style removal intensity (SRI). Treatments consisted in removing the styles of two, four(always the most developed), or all flowers in each cluster. Flower density was used as a covariate in an analysis of covariance to account for differences in flower densities in response to SRI treatments. In all experiments the covariate was not significant; therefore, SRI effect was not affected by flower density. `Blanquilla' and `Conference' had similar responses to treatments, so that when at least three flowers are susceptible to be openly pollinated, fruit set, seed content, and cluster yield were similar to control clusters, therefore the growth potential of fruit from partially damaged clusters in their most developed flowers is similar to undamaged open pollinated clusters. The reduced set of parthenocarpic clusters implies yield reductions ranging between 40% and 60% in `Conference', and up to about 60% in `Blanquilla'.

The apical or king (K) flower in the apple (Malus ×domestica L. Borkh.) cluster usually develops and blooms first and also has a greater sink potential. For this reason, resources are primarily used by the K fruit, and this is also one of the reasons why most thinning practices tend to favor K fruit set. However, it is not always possible to retain the K flower and remove the lateral ones. This study was undertaken to determine if the removal of the most developed flowers in the cluster influences yield or quality compared to that obtained in a whole cluster. The treatments were made in `Golden Delicious' and `Royal Gala' apple cultivars, within a wide range of flower densities for each cultivar. The factor tested was the intensity of flower removal (FRI); the treatments consisted in removing one, two, or three flowers in each cluster. Flower density was used as a covariate in an analysis of covariance to account for differences in flower densities in response to FRI treatments. In all experiments the covariate was not significant; therefore FRI effect was not affected by flower density. `Golden Delicious' and `Royal Gala' had similar responses to flower removal, so that when at least three flowers in a cluster remained, fruit set and cluster yield were similar to whole clusters. Only when two or fewer poorly developed flowers remained after FRI treatments, yield was reduced by as much as 25%. Fruit from FRI clusters were even heavier than those from whole clusters, due to reduced competition among the fruit, so that the growth potential of fruit from the first and second lateral flowers was similar to clusters with K fruit, in clusters where the K flower had been removed.

The influence of the species in spring frost sensibility was determined for the Prunus species peach (P. persica (L.) Batsch), sweet cherry (P. avium L.), almond (P. dulcis (Mill.) Webb/P. amygdalus Batsch), japanese plum (P. salicina Lindl.), and blackthorn (P. spinosa L.). The confidence intervals for lethal temperatures of 10% (LT₁₀) and 90% (LT₉₀) bud injury were also determined. In 2000 and 2001, seven frost treatments were made for each one of the phenological stages comprised between B (first swell) and I (jacket split) in two cultivars per each species. The relationships between frost temperature and the proportion of frost damaged buds for each cultivar, year, and phenological stage were adjusted to linear regression models. The 95% confidence intervals were also calculated. The spring frost hardiness order of the species, from the least to most hardy, was as follows: sweet cherry, almond, peach, japanese plum, and blackthorn. Despite the highly homogeneous nature of the frost and bud characteristics, the temperature range for a given injury degree was quite broad, since the confidence interval's breadth for LT₁₀ was as high as about 3 °C and as high as about 6 °C for LT₉₀. Consequently, when critical temperatures are used in making decisions as to when to begin active frost protection, a prudent measure would be to take the temperature references from the upper limits in the confidence intervals.

A collection of 141 old and local Spanish accessions of pear (Pyrus communis) from the Escuela Técnica Superior de Ingeniería Agraria-Universidad de Lleida (ETSIA-UdL) Pear Germplasm Bank in Lleida, Spain, were studied using a set of eight microsatellite markers to estimate the genetic diversity of the collection, to identify the genetic structure and relationships among its accessions, and to establish a representative core collection. An additional set of 13 well-known pear cultivars, currently grown in Spain and which represent a wide genetic diversity, were added as reference. The eight simple sequence repeat (SSR) loci amplified 97 alleles, with nine to 15 alleles per locus, and with the expected heterozygosity ranging from 0.65 to 0.89. All of the accessions except for 16 had at least one of the 48 rare alleles (frequency < 0.05) identified, and seven unique alleles were found in six accessions. Fifteen accessions were identified as synonyms and were excluded from the analysis. Genetic analyses performed by hierarchical clustering, Bayesian model-based clustering, and factorial correspondence analysis supported the existence of three groups among the accessions with moderate [fixation index (F_ST) = 0.074], but significant, differentiation. As a whole, most of the germplasm (about 75%) curated at the collection showed its genetic distinctness with respect to the main pear cultivars used in European orchards. In fact, most reference cultivars were included in one single cluster that, moreover, had the lowest genetic diversity and allelic richness, in spite of having been chosen as heterogeneous material from different origins. The obtained results were also used to create a core collection with 35 accessions constituting an efficient and accessible entry point in the ETSIA-UdL pear collection for breeding and research communities.